pam-krb5 3.6

I'm still feeling rather swamped, and fighting off a cold isn't helping
with energy levels, but I'm slowly making progress. I'm on target for
having a first release of the wallet finished around the first of October,
and I'm starting to clear my backlog of pending patches and fixes for the
other packages I maintain.

I tracked down some segfaults we were seeing on Red Hat x86_64 systems with
unknown users and fixed that bug, fixed the two outstanding Debian bugs in
libpam-krb5, and finally added support for prompting the user for a
Kerberos principal to authenticate as, separate from the local account.
That plus some fixes on Solaris and some other bug fixes are in this
release. It's been a long time since the previous release, although the
code is stabilizing.

I'd still like to do a major code cleanup pass and then add a test suite,
but that's going to be hard, particularly the latter. Not sure when I'm
going to have time.